Some wireless communication networks, and in particular cellular networks, use communication protocols that define frames in time domain. For example, Worldwide Interoperability for Microwave Access (WiMAX) networks may operate in a Time Division Duplex (TDD) or a Frequency Division Duplex (FDD) mode. Both of these modes transmit data in time frames. In TDD operation, uplink (UL) and downlink (DL) transmission is carried out on the same frequency while alternating between uplink and downlink subframes. In FDD operation, uplink and downlink subframes are transmitted on separate frequencies.
The original WiMAX standard, IEEE 802.16, specified WiMAX in the 10-66 GHz range. More recently, IEEE 802.16a added support for the 2-11 GHz range, and IEEE 802.16e (approved as IEEE 802.16-2005 and amended as IEEE 802.16-REV2) extended WiMAX to mobile applications. In the context of the present patent application and in the claims, the term “802.16” is used to refer collectively to the original IEEE 802.16 standard and all its variants and extensions, unless specifically noted otherwise.
The WiMAX standard defines both TDD and FDD frame structures. In TDD, the frame structures alternate between DL and UL subframes, whereas in FDD transmission in each direction is carried out on a separate frequency. In either TDD or FDD operation, the frames may be partitioned into zones, which correspond to different sub-channelization schemes. Section 8.3.4.1 of the IEEE 802.16-REV2 standard addresses the FDD frame structure. Section 8.3.4.2 of the standard addresses the TDD frame structure and its division into zones.